1. Field of the Invention
The invention relates generally to the field of optical modulators and more particularly to a distributed amplifier optical modulator for use in optoelectronic integrated circuits.
2. Description of the Related Art
Optical fibers have been widely used for the propagation of optical signals, especially to provide high speed communication links. Optical links using fiber optics have many advantages compared to electrical links. These advantages include large bandwidth, high noise immunity, reduced power dissipation, and reduced crosstalk. Fiber optic communication links can operate with carrier frequencies in the THz range. In communication systems where optical fibers are used to transport optical communication signals, various optoelectronic devices are used to control, modify, and process the optical signals.
An integrated optical modulator is one such component of an optical communication system. Certain optical modulators use an electrical signal to modulate some property of an optical wave, such as the phase or the amplitude. A modulated optical wave can be sent on a fiber optic link or processed by other optical or optoelectronic devices.
Integrated optoelectronic devices made of silicon are highly desirable since they can be fabricated in the same foundries used to make VLSI integrated circuits. Optoelectronic devices integrated with their associated electronic circuits can eliminate the need for more expensive hybrid optoelectronic circuits. Optoelectronic devices built using a standard CMOS process have many advantages, including high yields, low fabrication costs, and continuous process improvements.
Distributed amplifier optical modulators have been suggested that use a plurality, e.g., k modulators connected in series disposed on one of a variety of semiconductor substrates or wafers. An electrical signal propagating in a microwave transmission line in such distributed amplifier modulators is tapped off of the transmission line at regular intervals and is amplified by k distributed amplifiers which output the electrical signal to a respective one of the k modulators. These distributed amplifier modulators can have much higher modulating speeds than a comparable single lumped element modulator, as the distributed arrangement allow the input capacitance of the distributed amplifier blocks to be absorbed into the characteristic impedance of the input transmission line. The distributed amplifier modulators driving a plurality of lumped modulator elements can also have lower power consumption than comparable traveling wave modulators having a terminated output transmission line because no power is dissipated in the termination resistance of the output transmission line. However, the speed, performance reliability, and the size of the distributed amplifier modulators can be improved.